The invention relates to a turboramjet engine having a ram air duct constructed between an outer duct wall and a housing-type shrouding of a basic turbo-engine, and having shut-off devices by means of which the ram air duct is shut off when the basic engine is switched on and the ramjet engine is switched off, while at the same time releasing intake air into the basic engine on the air supply side.
Recently, combined turboramjet engines have regained importance, specifically within the scope of so-called "hypersonic flight concepts" with an extremely high spectrum of application from takeoff to high supersonic speed at high flight altitudes (up to an altitude of approximately 30 km). In this case, the hypersonic flight concepts, among other things, include a space flight aggregate concept (Sanger Project) which, as described in the following, amounts to a two-stage concept. The first stage is to be carried out by a flight aggregate operating only within the atmosphere, while the second stage is based on a useful-load flight aggregate which is taken along "piggyback" by the mentioned flight aggregate. For the purpose of space missions, in the upper range of the atmosphere the useful-load flight aggregate is to independently continue on the flight path assigned to it by means of a suitable rocket propulsion system. The flight aggregate responsible for the first stage can therefore return and be reused and carries out starts and landings like a conventional airplane.
In the case of combined turboramjet engines which are to be used for example for a flight aggregate of this type generally, when a flying speed of approximately Mach 3 is reached, the turbojet engine is to be switched off continuously, and the respective ramjet propulsion is to be switched on continuously so that, by means of the latter alone, desired high supersonic or hypersonic speeds are reached of up to Mach 4.5 or even more. Flying speeds of approximately Mach 2 or even more may be achieved in this case in the combined operation of "jet engine with a switched-on afterburner". The afterburner, which for this purpose is advantageously connected behind the jet engine part and is acted upon possibly by a combination of compressor or fan air and engine exhaust gas, by means of the connection of additional fuel injection devices together with flame stabilizers, may form the propulsion system for the ramjet operation, with a correspondingly proportioned exclusive ambient-air supply when the turbojet engine part is switched off. With a correspondingly adapted inlet and propelling-nozzle geometry, in the case of the concerned engine, the basic turbo-engine must therefore be switched off or shut down in the hypersonic operation, the required ram air then acting upon the exterior ram-air duct. This ram air may, for example, be supplied to the supplementary combustion chamber for the ramjet operation downstream of the basic turbo-engine end.
In this case the required shut-off device or devices of the basic engine part are extremely important. In the shut-off or blocked position of the basic engine during the ramjet operation, the basic engine must be impaired as little as possible by the comparatively high temperatures (approximately 1,700.degree. C.) of the ram air. This also applies to the shut-off devices themselves which must be constructed to be correspondingly robust and operationally reliable but which must nevertheless ensure at the same time that, for example, in the subsonic operation, an optimal aerodynamically perfect intake air supply is possible from the engine inlet to the basic turbo-engine in correspondingly proportioned quantities.
For the shutting-off or exposing, as the case may be, of the basic turbo-engine on the air supply side, the use of axially adjustable drop-shaped central bodies in the direction of the axis of the engine has been provided, for example, in combination with axially adjustable annular slide plates. The latter has the purpose of exposing or shutting off, as the case may be, the supply of ram air into the ram air duct in coordination with the adjustment by the central body. This type of a concept requires a comparatively large constructional widening of the circumference of the whole engine system in order to ensure the air inflow surfaces and paths into the ram air duct, that are required from case to case, but particularly to the compressor of the basic engine--in this case, therefore downstream of the largest diameter of the central body, among other things, in view of the required flow rates and flow Mach numbers. The mentioned constructional widening of the constructional circumference has the disadvantage of an increased aerodynamic frontal-area resistance and component weight. The reason for the latter is, among other things, also the construction of the central body itself. This type of a central body--whether it is arranged in an axially slidable or stationary manner--is an always present interference body resulting in aerodynamic losses, particularly as far as the release position of the intake air supply into the compressor of the basic turbo-engine is concerned.
It is an object of the invention to provide an engine of the initially mentioned type which, particularly in view of the construction and arrangement of the shut-off devices, while the constructional widening of the engine (diameter) is comparatively slight, permits an aerodynamically optimal charging of air to the ram air duct while the basic engine is shut off, or of the basic engine (compressor) while the ram-air duct is shut off.
According to the invention, the mentioned object is achieved according to preferred embodiments of the invention by providing an arrangement wherein an upstream axial extension of the ram air duct ends in front of a compressor-side front end of a basic turbo-engine on the inlet side,
wherein the shrouding forms an air shaft which in the direction of the inlet-side end of the ram air duct is widened in a polygonal manner,
wherein the shrouding has breakthroughs on the inlet-side end of the ram air duct,
and wherein the shut-off devices are flaps which are pivotally arranged at the breakthroughs and which, when the ramjet engine is switched on, expose the break-throughs and in the process form a shut-off body of the air shaft which is folded together symmetrically acutely with respect to the ram air flow.
It is an advantage that is very important to the invention that the flaps are at the same time shut-off devices of the basic engine and of the ram-air duct. In this case, when only the basic turbo-engine is operative and the flaps are moved into the breakthroughs, a free flow cross-section for the intake air in the intake channel is developed which, in the axial direction, is not impaired by any mounted parts. By means of even only two square or rectangular flaps which acutely or in a roof shape are folded together as an extended plane of symmetry of the engine, the basic engine can be shut-off during the ramjet operation and, in the process, the ram air flow can be uniformly distributed in the direction of the thus exposed breakthroughs. In one contemplated embodiment of the invention, two breakthroughs are provided which are laterally opposite one another and are connected by wa of the locally assigned inlet-side end of the ram air duct with its contour extending along the overall circumference. In addition, the two flaps, with their exterior edges, would also have to be arranged to be sealingly movable along linear wall surfaces of the four-cornered shrouding.
The additional use of triangular flaps which is possible according to certain preferred embodiments of the invention permits breakthroughs that are essentially uniformly assigned on all sides, are arranged along the circumference in the shrouding, and are connected with the inlet-side end of the ram air duct.
In preferred embodiments of the invention, the ram air duct is therefore constructed to be ring-shaped with the part of the shrouding forming the air shaft changing to a four-cornered or polygonal cross-section not before reaching a transition area to the inlet-side end of the ram air duct. The latter is also true in connection with the geometrically correspondingly adapted residual wall ends of the outer circumferential wall for the ram air duct. In other words, in connection with the arrangement of the shut-off devices and breakthroughs, only a corner-side widening of the engine is obtained from the at first purely circular outer structure of the engine (basic turbo-engine) in the direction of the upstream end of the ram air duct. Thus, according to the invention, the breakthroughs and flaps are preferably arranged or assigned to one another on segments of the polygonal or four-cornered section of the shrouding which has a straight surface in the axial and circumferential direction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.